This invention relates to loudspeaker systems and, more particularly, to loudspeaker systems for generating hemispherical sound wave patterns.
Loudspeakers are widely used for providing projection of voice and music in a variety of areas and for numerous purposes. One area in which loudspeakers are particularly important and have had substantial difficulty in providing good results is in large public areas. In such locations, the use of conventional loudspeakers is common, but there are difficulties because of the directional nature of the speakers"" sound projection. As a result, in order to assure maximum coverage, numerous or multiple speakers are employed with overlapping coverage areas which requires proper engineering and often considerable expense to attain the desired results.
In an attempt to reduce the necessity of having numerous loudspeaker components installed to provide the desired coverage, loudspeakers having a hemispherical coverage pattern have been developed. Although many of these prior art loudspeakers had been able to provide a projection of voice and music over a wider listening area, numerous problems have continued to exist in producing products which achieve a true full frequency hemispherical sound projection pattern from a single overhead sound source.
One of the principal problems which has plagued prior art spherical loudspeakers as well as conventional loudspeakers centers on the physical characteristics of acoustic wave patterns. In this regard, audio frequencies essentially occupy 11 octaves of the electromagnetic spectrum, with acoustical wave lengths varying across a ratio of more than 2000 to 1 (about 113 feet to about xc2xd in.). In most applications, a more reasonable and workable ratio is 1000 to 1 (about 56 feet to 0.68 inches). Regardless of which ratio is employed, it is apparent, due to their very nature, that these extremes of wavelength energy require the application and use of completely different areas and aspects of the laws of physics.
Another problem inherent in providing optimum projection of voice and music is the fact that lower frequencies of the audio spectrum produce spherical waves which tend to be fluid in nature and difficult to control in terms of shaping and directing. Furthermore, higher frequencies develop planar waves which exhibit directional characteristics and are, by their very nature, not easily dispersed or diffused into broad coverage patterns. Finally, midrange frequencies produce various combinations of these two extremes.
In attempting to overcome these prior art problems, while also providing maximum area coverage, spherical loudspeaker systems with shaped dishes or xe2x80x9creflectorsxe2x80x9d suffer from one or more shortcomings. One such common problem is a severe decrease of high frequency energy distribution at the wider points of coverage, typically beginning at about 45 degrees from the central axis. Another common problem is a significant increase in phase distortion from unwanted multiple reflections occurring between the sound source and the reflector, as well as a significant increase intermodulation distortion due to the remodulation of one-wave by another of a different frequency. Finally, high intensity lobes of acoustic energy are often produced directly on axis with the reflector, expanding as wide as 20 to 30 degrees from the central axis.
By employing the present invention, all of the difficulties and drawbacks of prior art loudspeaker constructions are eliminated and a true hemispherical sound pattern producing loudspeaker system is achieved which controls and shapes the ultimate acoustical waveform produced thereby. In the present invention, a loudspeaker system is provided which incorporates a spherically shaped loudspeaker and/or closure containing one or more drivers or speaker motors. In most applications, a high frequency speaker or driver is employed in combination with a low frequency driver. In addition, a uniquely constructed reflector is employed which is mounted in cooperative association with the spherical enclosure. In this way, the system of the present invention controls and distributes the acoustical energy of the driver, while shaping the acoustical energy field in a true hemispherical pattern, within the systems power bandwidth. By employing the present invention, the point of summation of the hemispherical pattern is approximately eight times the diameter of the reflector, thereby achieving the desired hemispherical polar coverage patterns.
In the preferred construction, the reflector of the present invention is designed to be rigidly and mechanically attached to the spherical cabinet forming the loudspeaker or, alternatively, built into the construction of the sphere during the fabrication or molding process as a homogeneous or integral component thereof. The center or apex of the reflector is intended to be physically close to and acoustically intimately coupled with the geometric center of the driver""s diaphragm.
In addition, the reflector also incorporates uniquely designed and shaped vanes formed on the surface thereof which enhance the output from the reflector by distributing the high frequency energy out to the roader angles of the coverage pattern. In the preferred embodiment, the vanes are constructed as secondary reflector vanes and comprise an exponential cross-section that is continuously variable over their entire length. In the preferred construction, the axial profile of the vanes is also exponential.
By employing the present invention, a loudspeaker system is achieved which controls and defines the wave shape and coverage patterns of the various frequency bandwidths, utilizing the natural characteristics of the wave itself, with no forced or artificial control. Using the three basic elements of a loudspeaker systemxe2x80x94(1) the driver, (2) the spherical enclosure, and (3) the reflectorxe2x80x94in a unique integral design, a synergistic interaction of these components is achieved which produces true hemispherical coverage patterns across the entire rated power bandwidth of the loudspeaker.
The invention accordingly comprises an article of manufacture possessing the features, properties, and relation of elements which will be exemplified in the article hereinafter described, and the scope of the invention will be indicated in the claims.